Magnetic detection apparatus

ABSTRACT

A magnetic detection apparatus includes a first comparison circuit that waveform-shapes the amplitude of a detection signal from magneto-electric transducers by DC coupling, a third comparison circuit that waveform-shapes the detection signal by AC coupling, an oscillation circuit having a natural frequency, a control circuit that counts the output of the first comparison circuit by using the oscillation means, and a selection circuit that selects the output of the first comparison means and the output of the second comparison means. The control circuit counts rising from the next rising or falling from the next falling of an output rectangular wave of the first comparison circuit, and provides output to the selection circuit at the time point at which the count value reaches a desired value. The selection circuit selects and outputs the output rectangular wave of the first comparison circuit or the third comparison circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic detection apparatus thatdetects the speed of a moving member by using a magnetic sensor elementgroup.

2. Description of the Related Art

For example, there is a scheme in which a bridge circuit is configuredby forming electrodes at each terminal of a magnetic reluctance element(magneto-electric transducer), a power source of a constant voltage anda constant current is connected between two electrodes facing each otherin the bridge circuit, variation in a resistance value of the magneticreluctance element is converted into voltage variation, and variation ina magnetic field applied to the magnetic reluctance element is detected(for example, refer to JP-A-2007-192733).

Hereinafter, the conventional magnetic detection apparatus disclosed inJP-A-2007-192733 will be described with reference to the accompanyingdrawings.

FIGS. 14A and 14B are schematic diagrams illustrating the configurationof a magnetic circuit of the conventional magnetic detection apparatus,wherein FIG. 14A is a perspective view of the magnetic circuit and FIG.14B is a top view of the magnetic circuit.

In FIGS. 14A and 14B, the conventional magnetic detection apparatusincludes a magnet 1 that generates a bias magnetic field, and aprocessing circuit unit 2 provided on the magnet 1 and having circuitsformed on a board. The processing circuit unit 2 includes an IC chip inwhich magnetic reluctance elements 21 a and 21 b serving as a magneticsensor are integrally formed as segments with each other. The magneticreluctance elements 21 a and 21 b, for example, are arranged to face amagnetic moving member 3 having protrusions formed at the peripheraledge of a disc to change the magnetic field, and are arranged inparallel to the movement direction of the magnetic moving member 3.Reference numeral 4 indicates a rotating axis of the magnetic movingmember 3, the magnetic moving member 3 rotates in synchronization withthe rotation of the rotating axis 4, and the resistance values of themagnetic reluctance elements 21 a and 21 b change according to thedisplacement of the magnetic moving member 3.

In addition, in FIGS. 14A and 14B, the magnetic reluctance elements 21 aand 21 b are shown by one black block, respectively. However, magneticreluctance elements may be arranged to detect predetermined variation ina magnetic field.

FIG. 15 is a circuit configuration diagram illustrating theconfiguration of a processing circuit unit of the conventional magneticdetection apparatus using magnetic reluctance elements. FIGS. 16 and 17are timing charts illustrating operation waveforms according to theprocessing circuits of FIG. 15, wherein FIG. 16 illustrates operationwaveforms of each signal when the rotation number of a magnetic movingmember 3 is low, and FIG. 17 illustrates operation waveforms of eachsignal when the rotation number of the magnetic moving member 3 is high.

In FIG. 15, the conventional magnetic detection apparatus includes abridge circuit 10, a first comparison circuit 31, a second comparisoncircuit 32, a third comparison circuit 33, a logic processing circuit34, transistors 12 and 13 for output, and an output terminal Vout. Thebridge circuit 10 configures a sensor that detects magnetic fieldstrength, and includes two magnetic reluctance elements 21 a and 21 bserving as a magneto-electric transducer. As described above, in thebridge circuit 10, the resistance values of the magnetic reluctanceelements 21 a and 21 b change according to the displacement of themagnetic moving member 3, resulting in the variation in the voltage of adetection signal C of the bridge circuit 10.

The detection signal C of the bridge circuit 10 is input to the firstcomparison circuit 31 and the second comparison circuit 32, and is alsoinput to the third comparison circuit 33 through a high-pass filterincluding a capacitor 22 and a resistor 23.

The first comparison circuit 31 has a first comparison level VR1,waveform-shapes the amplitude of the detection signal C by DC coupling,and outputs a rectangular wave signal E.

The second comparison circuit 32 has a second comparison level VR2different from the first comparison level VR1, waveform-shapes theamplitude of the detection signal C by the DC coupling, and outputs arectangular wave signal F.

The third comparison circuit 33 has a third comparison level VR3 betweenthe first comparison level VR1 and the second comparison level VR2,waveform-shapes the amplitude of the detection signal C after ACcoupling, and outputs a rectangular wave signal G.

Hereinafter, the first to third comparison levels VR1 to VR3 will besimply referred to as “comparison levels”, respectively.

The detection signal Cis converted into the rectangular wave signal Ethrough a comparison with the comparison level VR1 in the firstcomparison circuit 31, and is converted into the rectangular wave signalF through a comparison with the comparison level VR2 in the secondcomparison circuit 32. Further, the detection signal C is converted intoa voltage signal D after the AC processing through the high-pass filterincluding the capacitor 22 and the resistor 23, and then is convertedinto the rectangular wave signal G through a comparison with thecomparison level VR3 in the third comparison circuit 33.

The output signals E to G of the first to third comparison circuits 31to 33 are logically processed by the logic processing circuit 34, andthen are output as a final output signal K through the transistors 12and 13.

The logic processing circuit 34 includes a first transistor 41 and athird transistor 43 serially inserted between a supply voltage VCC and aground, a second transistor 42 and a fourth transistor 44 seriallyinserted between the supply voltage VCC and the ground, and a fifthtransistor 45 inserted between the supply voltage VCC and the ground.The logic processing circuit 34 inputs the output signal of the secondtransistor 42 to the transistor 12 for output as the final outputsignal.

Hereinafter, the first to fifth transistors 41 to 45 will be simplyreferred to as “transistors”, respectively.

The transistor 41 is turned on and off by the output signal E of thefirst comparison circuit 31, and the transistor 42 is turned on and offby the output signal of the transistor 41. The transistor 43 is seriallyconnected to the transistor 41 and is turned on and off by the outputsignal G of the third comparison circuit 33. The transistor 45 is turnedon and off by the output signal F of the second comparison circuit 32.The transistor 44 is serially connected to the transistor 42 and isturned on and off by the output signal of the transistor 45.

That is, the transistor 41 has an emitter terminal connected to acollector terminal of the transistor 43, a collector terminal (an outputterminal) connected to a base terminal of the transistor 42 while beingconnected to the supply voltage VCC through a resistor, and a baseterminal that receives the rectangular wave signal E. Further, thetransistor 42 has a base terminal connected to the output terminal ofthe transistor 41, an emitter terminal connected to the collectorterminal of the transistor 44, and a collector terminal (an outputterminal) connected to the supply voltage VCC through a resistor andserving as the final output terminal.

In addition, the transistor 45 has an emitter terminal connected to theground, a collector terminal (an output terminal) connected to a baseterminal of the transistor 44 while being connected to the supplyvoltage VCC through a resistor, and a base terminal that receives therectangular wave signal F. Moreover, the transistor 44 has an emitterterminal connected to the ground, a collector terminal connected to theemitter terminal of the transistor 42.

In the logic processing circuit 34 having the above configuration, thetransistors 41 and 43 configure an inversion input-type AND gate, thetransistors 42 and 44 configure an inversion input-type AND gate, andthe transistor 45 configures an inverter.

In addition, the transistors 12 and 13 for output configure an amplifierfor amplifying the final output signal K.

Accordingly, the final output signal K has a logic level varyingdepending on the combination of the logic levels of the output signals Eto G of the first to third comparison circuits 31 to 33 as shown in (1)to (8) below. Herein, “H” indicates a high level of the rectangular wavesignal and “L” indicates a low level of the rectangular wave signal.

(1) when E, G and F are “H, H and H”, K=“H”

(2) when E, G and F are “H, H and L”, K=“H”

(3) when E, G and F are “H, L and H”, K=“H”

(4) when E, G and F are “H, L and L”, K=“L”

(5) when E, G and F are “L, H and H”, K=“H”

(6) when E, G and F are “L, H and L”, K=“L”

(7) when E, G and F are “L, L and H”, K=“H”

(8) when E, G and F are “L, L and L”, K=“L”

FIG. 16 illustrates operation waveforms of signals C′ to G′, and K′ whenthe magnetic moving member 3 is in a low rotation state, and FIG. 17illustrates operation waveforms of signals C to G, and K when themagnetic moving member 3 is in a high rotation state.

In the case of the low rotation, single quotes are attached to eachsignal. That is, the detection signal C becomes C′, the voltage signal Dafter the AC processing becomes D′, the rectangular wave signal Ebecomes E′, the rectangular wave signal G becomes G′, the rectangularwave signal F becomes F′, and the final output signal K becomes K′.

In FIG. 16, as apparent from the combination of the voltage level “H andL” of the signals E′, F′, G′ and K′, the rising timing “L→H” of thefinal output signal K′ at the time of the low rotation is the same asthe rising timing of the rectangular wave signal E′ from the firstcomparison circuit 31.

Further, the falling timing “H→L” of the final output signal K′ is thesame as the falling timing of the rectangular wave signal F′ from thesecond comparison circuit 32.

Meanwhile, in FIG. 17, the rising timing and the falling timing of thefinal output signal K at the time of the high rotation are the same asthe rising timing and the falling timing of the rectangular wave signalG from the third comparison circuit 33, respectively. That is, when themagnetic moving member 3 is in the low rotation state, the outputsignals E and F after the DC processing from the first comparisoncircuit 31 and the second comparison circuit 32 are used. When themagnetic moving member 3 is in the high rotation state, the outputsignal G after the AC processing from the third comparison circuit 33 isused.

At this time, since the phase difference between the rectangular signalsE and F after the DC processing from the first comparison circuit 31 andthe second comparison circuit 32 and the rectangular signal G after theAC processing from the third comparison circuit 33 is always equal to orless than ¼ period, the final output signal K can be achieved withoutany difficulty regardless of the rotation states of the magnetic movingmember 3. Further, the switching timing of the case of applying the DCprocessing of the first comparison circuit 31 and the second comparisoncircuit 32 and the case of applying the AC processing of the thirdcomparison circuit 33 can be arbitrarily set by adjusting the circuitconstant of the capacitor 22 and the resistor 23 constituting thehigh-pass filter.

However, in the conventional apparatus disclosed in JP-A-2007-192733 asdescribed above, as shown in FIG. 18, when the detection signal C isshifted upward and exceeds the comparison level VR2, the rising timingof the final output signal K is the same as the rising timing of therectangular wave signal E from the first comparison circuit 31. Further,the falling timing of the final output signal K is the same as thefalling timing of the rectangular wave signal G from the thirdcomparison circuit 33.

Therefore, in the conventional magnetic detection apparatus as shown inFIG. 18, when the shift amount of the detection signal C is large, itmay be difficult to determine setting values of the comparison levelsVR1 to VR3 and to detect the accurate position of an object to bedetected.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the present invention toprovide a magnetic detection apparatus capable of detecting the accurateposition of an object to be detected even if the shift amount of adetection signal is large because temperature offset occurs in variationin the voltage of magneto-electric transducers due to variation in thetemperature coefficient of the magneto-electric transducers, variationin the strength of a magnetic field applied to the magneto-electrictransducers, and the like.

According to an aspect of the invention, there is provided a magneticdetection apparatus provided with a sensor including magneto-electrictransducers for detecting a magnetic field, the magnetic detectionapparatus including: a first comparison means that waveform-shapes adetection signal from the magneto-electric transducers by DC coupling; asecond comparison means that waveform-shapes the detection signal fromthe magneto-electric transducers by AC coupling; an oscillation meanshaving a natural frequency; a control means that counts output of thefirst comparison means or output of the second comparison means by usingthe oscillation means; and a selection means that selects the output ofthe first comparison means and the output of the second comparison meansin response to a count value of the control means.

In accordance with the magnetic detection apparatus according to thepresent invention, even when large variation occurs in the output ofmagneto-electric transducers due to variation in a temperaturecoefficient of the magnetic reluctance elements, variation in thestrength of a magnetic field applied to the magnetic reluctanceelements, and the like, the position of an object to be detected can beaccurately detected regardless of the shift amount of the detectionsignal.

The foregoing and other object, features, aspects, and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit configuration diagram illustrating processingcircuits of a magnetic detection apparatus according to a firstembodiment of the present invention;

FIG. 2 is a timing chart illustrating operation waveforms at the time oflow rotation of a magnetic moving member in a magnetic detectionapparatus according to a first embodiment of the present invention;

FIG. 3 is a timing chart illustrating operation waveforms at the time ofhigh rotation of a magnetic moving member in a magnetic detectionapparatus according to a first embodiment of the present invention;

FIG. 4 is a timing chart illustrating operation waveforms whentemperature offset occurs in variation in a voltage of a detectionsignal in a magnetic detection apparatus according to a first embodimentof the present invention;

FIG. 5 is a circuit configuration diagram illustrating processingcircuits of a magnetic detection apparatus according to a secondembodiment of the present invention;

FIG. 6 is a waveform diagram explaining switching of a rectangular wavesignal of a first comparison circuit and a rectangular wave signal of athird comparison circuit in a logic circuit according to a secondembodiment of the present invention;

FIG. 7 is a waveform diagram explaining switching of a rectangular wavesignal of a first comparison circuit and a rectangular wave signal of athird comparison circuit in a logic circuit according to a secondembodiment of the present invention;

FIG. 8 is a top view of a magnetic moving member in a magnetic detectionapparatus according to a second embodiment of the present invention;

FIG. 9 is an operation waveform diagram when using a magnetic movingmember of FIG. 8 in a magnetic detection apparatus according to a secondembodiment of the present invention;

FIG. 10 is a flow diagram illustrating an output selection state of afirst comparison circuit and a third comparison circuit in a magneticdetection apparatus according to a third embodiment of the presentinvention;

FIG. 11 is a circuit configuration diagram illustrating processingcircuits of a magnetic detection apparatus according to a fourthembodiment of the present invention;

FIG. 12 is an operation waveform diagram in a magnetic detectionapparatus according to a fourth embodiment of the present invention;

FIG. 13 is an operation waveform diagram in a magnetic detectionapparatus according to a fourth embodiment of the present invention;

FIGS. 14A and 14B are schematic diagrams illustrating the configurationof a magnetic circuit of the conventional magnetic detection apparatus

FIG. 15 is a circuit configuration diagram illustrating theconfiguration of processing circuits of the conventional magneticdetection apparatus;

FIG. 16 is a timing chart illustrating operation waveforms of theconventional magnetic detection apparatus;

FIG. 17 is a timing chart illustrating operation waveforms of theconventional magnetic detection apparatus; and

FIG. 18 is a timing chart illustrating operation waveforms when theshift amount of a detection signal is large in the conventional magneticdetection apparatus.

DESCRIPTION OF PREFERRED EMBODIMENT First Embodiment

Hereinafter, a magnetic detection apparatus according to the firstembodiment of the present invention will be described with reference tothe accompanying drawings.

FIG. 1 is a circuit configuration diagram illustrating the configurationof a processing circuit unit of the magnetic detection apparatusaccording to the first embodiment of the present invention, and the samereference numerals are used to designate elements the same as or similarto those of the conventional diagram (refer to FIG. 15). FIGS. 2 and 3are timing charts illustrating operation waveforms according to theprocessing circuits of FIG. 1, wherein FIG. 2 illustrates operationwaveforms of each signal when the rotation number of a magnetic movingmember 3 is low, and FIG. 3 illustrates operation waveforms of eachsignal when the rotation number of the magnetic moving member 3 is high.

Further, the configuration of a sensor unit including magneticreluctance elements 21 a and 21 b is the same as that shown in FIG. 14.

In FIG. 1, the magnetic detection apparatus according to the firstembodiment of the present invention includes a bridge circuit 10, afirst comparison circuit 31, a third comparison circuit 33, a logicprocessing circuit 50, transistors 12 and 13 for output, and an outputterminal Vout. The bridge circuit 10 configures a sensor that detectsmagnetic field strength, and includes the two magnetic reluctanceelements 21 a and 21 b serving as a magneto-electric transducer. In thebridge circuit 10, the resistance values of the magnetic reluctanceelements 21 a and 21 b change according to the displacement of themagnetic moving member 3, resulting in the variation in the voltage of adetection signal C of the bridge circuit 10. The detection signal C ofthe bridge circuit 10 is input to the first comparison circuit 31, andis also input to the third comparison circuit 33 through a high-passfilter including a capacitor 22 and a resistor 23.

The first comparison circuit 31 has a first comparison level VR1,waveform-shapes the amplitude of the detection signal C by the DCcoupling, and outputs a rectangular wave signal E.

The third comparison circuit 33 has a third comparison level VR3,waveform-shapes the amplitude of the detection signal C after the ACcoupling, and outputs a rectangular wave signal G.

The detection signal C is converted into the rectangular wave signal Ethrough a comparison with the first comparison level VR1 in the firstcomparison circuit 31, is converted into a voltage signal D after ACprocessing through the high-pass filter including the capacitor 22 andthe resistor 23, and then is converted into the rectangular wave signalG through a comparison with the third comparison level VR3 in the thirdcomparison circuit 33.

The output signals E and G of the first and third comparison circuits 31and 33 are logically processed by the logic processing circuit 50, andthen are output as a final output signal K through the transistors 12and 13.

The logic processing circuit 50 includes an oscillator 51 having anatural oscillation frequency, a control circuit 52 and a selectioncircuit 53.

An output signal L of the oscillator 51 is input to the control circuit52. The control circuit 52 counts from the rising to the next rising orfrom the falling to the next falling of the rectangular wave signal E ofthe first comparison circuit 31 by using an oscillation signal L. Whenthe count value exceeds a desired count value, the control circuit 52outputs a control signal M at a low level. Further, when the count valueis equal to or less than the desired count value, the control circuit 52outputs a control signal M at a high level.

FIGS. 2 and 3 illustrate the operation waveforms when the control signalM is at the low level and the high level.

When the control signal M at the low level is output from the controlcircuit 52, the selection circuit 53 selects the output of therectangular wave signal E of the first comparison circuit 31. Further,when the control signal M at the high level is output from the controlcircuit 52, the selection circuit 53 selects the output of therectangular wave signal G of the third comparison circuit 33.

FIG. 4 illustrates the operation waveforms when temperature offsetoccurs in variation in the voltage of the detection signal C due tovariation in a temperature coefficient of the magnetic reluctanceelements 21 a and 21 b, variation in the strength of a magnetic fieldapplied to the magnetic reluctance elements 21 a and 21 b, and the like.

In FIG. 4, the first comparison level VR1 of the first comparisoncircuit 31 and the third comparison level VR3 of the third comparisoncircuit 33 are set to have the same value. Even if voltage offset of thedetection signal C is large, the rectangular wave signal E can be outputso long as the voltage offset is detected by one comparison level (i.e.,the comparison level VR1).

The magnetic moving member 3 may have a tooth shape or may also have amagnetization pattern. Further, the magnetic moving member 3 may be arotating member or a linear member. That is, the magnetic moving member3 may be a moving member having a movement direction arbitrarilydetermined.

Further, the sensor element may be a magneto-electric transducer such asa hall element, a magnetic reluctance (MR) element, a giant magneticreluctance (GMR) element and a tunnel type magnetic reluctance (TMR)element.

Furthermore, for the AC processing, the high-pass filter is used.However, a low-pass filter may also be used.

The magnetic detection apparatus according to the first embodiment ofthe present invention includes a first comparison means thatwaveform-shapes a detection signal from the magneto-electric transducersby DC coupling, a second comparison means that waveform-shapes thedetection signal from the magneto-electric transducers by AC coupling,an oscillation means having a natural frequency, a control means thatcounts output of the first comparison means or output of the secondcomparison means by using the oscillation means, and a selection meansthat selects the output of the first comparison means and the output ofthe second comparison means in response to the count value of thecontrol means, wherein the control means counts a time width of anoutput rectangular wave of the first comparison means or a time width ofan output rectangular wave of the second comparison means by using theoscillation means, and outputs a determination result to the selectionmeans when it is determined that the counted time width is a desiredtime width.

Consequently, even when variation in a temperature coefficient of themagnetic reluctance elements is large or variation in the strength of amagnetic field applied to the magnetic reluctance elements is large, ifthe variation is detected by one comparison level, any one ofrectangular wave signals after AC coupling or DC coupling can beselected and output, and the position of an object to be detected can beaccurately detected regardless of the shift amount of the detectionsignal.

Second Embodiment

FIG. 5 is a diagram illustrating the configuration of a processingcircuit unit of a magnetic detection apparatus according to the secondembodiment of the present invention, and the same reference numerals areused to designate elements the same as or similar to those of FIG. 1.

In FIG. 5, the magnetic detection apparatus according to the secondembodiment of the present invention includes the bridge circuit 10, thefirst comparison circuit 31, the third comparison circuit 33, a logicprocessing circuit 50A, the transistors 12 and 13 for output, and theoutput terminal Vout. The magnetic detection apparatus has a circuitconfiguration the same as that of the magnetic detection apparatusaccording to the first embodiment, except for the logic processingcircuit 50A, and performs a circuit operation the same as that of themagnetic detection apparatus according to the first embodiment.

In FIG. 5, the output signals E and G of the first and third comparisoncircuits 31 and 33 are logically processed by the logic processingcircuit 50A, and then are output as a final output signal K through thetransistors 12 and 13. The logic processing circuit 50A includes anoscillator 51 having a natural oscillation frequency, a control circuita54, a control circuit b55 and a selection circuit 53.

An output signal L of the oscillator 51 is input to the control circuita54 and the control circuit b55.

The control circuit a54 counts from the falling to the next falling orfrom the rising to the next rising of the rectangular wave signal E ofthe first comparison circuit 31 by using the oscillation signal L. Whenthe count value exceeds a desired count value, the control circuit a54outputs a control signal P at a low level. Further, when the count valueis equal to or less than the desired count value, the control circuita54 outputs a control signal P at a high level.

An output signal P of the control circuit a54 is input to the controlcircuit b55.

The control circuit b55 counts from the falling to the next falling orfrom the rising to the next rising of the rectangular wave signal E ofthe first comparison circuit 31. When the count value exceeds thedesired count value and the output signal P of the control circuit a54is at the low level, the control circuit b55 outputs a control signal Mat a low level.

Further, when the count value is equal to or less than the desired countvalue and the output signal P of the control circuit a54 is at the highlevel, the control circuit a54 outputs the control signal M at a highlevel.

However, when the count value exceeds the desired count value and theoutput signal P of the control circuit a54 is at the high level, thecontrol circuit b55 outputs the control signal M at the high level.Further, when the count value is equal to or less than the desired countvalue and the output signal P of the control circuit a54 is at the lowlevel, the control circuit a54 outputs the control signal M at the lowlevel.

FIGS. 6 and 7 are diagrams explaining switching of the logic processingcircuit 50A with respect to the rectangular wave signal E of the firstcomparison circuit 31 and the rectangular wave signal G of the thirdcomparison circuit 33.

For the purpose of convenience, a portion of the rectangular wavesignal, which exceeds the desired count value by the oscillation signalL, will be referred to as “DC”, and a portion of the rectangular wavesignal, which is less than the desired count value, will be referred toas “AC”.

In FIGS. 6 and 7, the DC and the AC are attached to the rectangular wavesignals. Further, for the purpose of convenience, “a1”, “b1” and thelike are attached to each waveform of the rectangular wave signals E, Gand K.

FIG. 6 illustrates the switching operation from the AC to the DC.

Since the rectangular wave signal E is switched into the DC at a4, thecontrol signal P is changed from the high level to the low level at thetiming just before a5 after a4 of the rectangular wave signal E.

Further, since the rectangular wave signal E is continued with the DC ata5, the control signal M is changed from the high level to the low levelat the timing just before a6 after a5 of the rectangular wave signal E.Consequently, in the output signal K, the signal of a6 is output at thetiming just before b6 after b5. That is, the output signal K is outputin such a manner that the signal of a6 is output after the DC indicatedby b4 and b5 is continued twice.

FIG. 7 illustrates the switching operation from the DC to the AC.

Since the rectangular wave signal E is switched into the AC at a4, thecontrol signal P is changed from the low level to the high level at thetiming just before a5 after a4 of the rectangular wave signal E.

Further, since the rectangular wave signal E is continued with the AC ata5, the control signal M is changed from the low level to the high levelat the timing just before a6 after a5 of the rectangular wave signal E.Consequently, in the output signal K, the signal of b6 is output at thetiming just before a6 after a5. That is, the output signal K is outputin such a manner that the signal of b6 is output after the AC indicatedby a4 and a5 is continued twice.

FIG. 8 is a top view of the magnetic moving member 5. The magneticmoving member 5 is a general magnetic moving member mounted on a vehicleto detect the rotation number. In FIG. 8, “T1” to “T8” are attached toprotrusions formed at the peripheral edge of a disc.

In the magnetic moving member 5 shown in FIG. 8, the tooth between T3and T4 has been extracted. The extraction of the tooth allows the angleof every one rotation of the magnetic moving member 5 to be detected.

FIG. 9 is an operation waveform diagram of the second embodiment usingthe magnetic moving member 5 of FIG. 8. The magnetic moving member 5rotates around the number rotation number at which switching of AC andDC is performed. Since the tooth between T3 and T4 of the magneticmoving member 5 has been extracted, the rectangular wave signal E is inan AC state at a3. However, the rectangular wave signal E is switchedinto the DC at a4, and then is switched into the AC at a5. As describedin FIGS. 5 to 7, in the magnetic detection apparatus according to thesecond embodiment, the output signal K is output in synchronization withthe output of the rectangular wave signal G, for example, in thesequence of b1, b2, b3, b4, b5, b6, b7 and b8. Even in the case of therotation number around the rotation number for determining the switchingof AC and DC, there is no output of the rectangular wave signal E inwhich the tooth extraction part (between T3 and T4) is in a DC state.

The magnetic detection apparatus according to the present invention isconfigured as mentioned above. Therefore, in relation to the rotationnumber around the rotation number set for the switching of AC and DC,when the magnetic moving member has the tooth extraction part, there isno exchange (chattering) of the rectangular wave signal E and therectangular wave signal G.

Third Embodiment

Hereinafter, a magnetic detection apparatus according to the thirdembodiment of the present invention will be described with reference tothe accompanying drawings.

The processing circuit unit of the magnetic detection apparatusaccording to the third embodiment of the present invention has aconfiguration the same as that of FIG. 1 according to the firstembodiment. That is, the magnetic detection apparatus according to thethird embodiment of the present invention includes a bridge circuit 10,a first comparison circuit 31, a third comparison circuit 33, a logicprocessing circuit 34, transistors 12 and 13 for output, and an outputterminal Vout. The magnetic detection apparatus performs a circuitoperation the same as that of the magnetic detection apparatus accordingto the first embodiment, except for a control circuit 52.

In FIG. 1, the output signal L of the oscillator 51 is input to thecontrol circuit 52.

The control circuit 52 counts from the falling to the next falling orfrom the rising to the next rising of the rectangular wave signal E ofthe first comparison circuit 31 by using the oscillation signal L. Thecontrol circuit 52 has two values A and B which are obtained byfrequency-converting the desired count value.

The frequency-conversion indicates a reciprocal of the counted timewidth.

In the case in which the selection circuit 53 selects the rectangularwave signal E of the first comparison circuit 31, when the count valuereaches the frequency value A, the control circuit 52 allows the controlsignal M to be changed from the low level to the high level. Further, inthe case in which the selection circuit 53 selects the rectangular wavesignal G of the third comparison circuit 33, when the count valuereaches the frequency value B, the control circuit 52 allows the controlsignal M to be changed from the high level to the low level.

FIG. 10 is a flow diagram illustrating the state in which the selectioncircuit 53 of the magnetic detection apparatus according to the thirdembodiment selects the output of the first comparison circuit 31 and theoutput of the third comparison circuit 33.

In FIG. 10, the frequency value A is set to be larger than the frequencyvalue B. Consequently, hysteresis may be added to the switchingfrequency of the first comparison circuit 31 and the third comparisoncircuit 33 by the selection circuit 53.

As described above, in accordance with the magnetic detection apparatusaccording to the third embodiment of the present invention, in relationto the rotation number around the rotation number set for the switchingof AC and DC, there is no exchange (chattering) of the rectangular wavesignal E and the rectangular wave signal G due to minute increase anddecrease in the rotation number of the magnetic moving member.

Fourth Embodiment

FIG. 11 is a diagram illustrating the configuration of a processingcircuit unit of a magnetic detection apparatus according to the fourthembodiment of the present invention, and FIGS. 12 and 13 are diagramsillustrating the operation waveforms of a peak-bottom circuit and anoffset circuit in the magnetic detection apparatus according to thefourth embodiment.

In FIG. 11, the magnetic detection apparatus according to the fourthembodiment of the present invention includes the bridge circuit 10, thefirst comparison circuit 31, the third comparison circuit 33, the logicprocessing circuit 50A, the transistors 12 and 13 for output, the outputterminal Vout, the peak-bottom circuit 61 and the offset circuit 62. Themagnetic detection apparatus has a circuit configuration the same asthat of the magnetic detection apparatus according to the secondembodiment, except for the peak-bottom circuit 61 and the offset circuit62, and performs an operation the same as that of the magnetic detectionapparatus according to the second embodiment.

The peak-bottom circuit 61 outputs a value (P+B)/m, which is obtained bydividing the sum (P+B) of a peak value P and a bottom value B of aninputted bridge signal C into m, to the offset circuit 62. Herein, m isan arbitrary numerical value.

Further, the offset circuit 62 performs desired digital offset on thebridge signal C such that the value (P+B)/m and the voltage value VR1approximate each other, thereby outputting a signal Q.

In addition, the peak-bottom circuit 61 and the offset circuit 62 may bereset using the rectangular wave signal E, the oscillator 51, or both ofthem.

FIG. 12 illustrates the transition state of convergence of the signal Qaccording to the operation of the peak-bottom circuit 61 and the offsetcircuit 62. In FIG. 12, m has a value of 2 (m=2).

The peak-bottom circuit 61 performs a reset operation at a desiredtiming to achieve a value, which is obtained by averaging a peak valueP1 and a bottom value B1 of the next signal C, that is, a value C1(=(P1+B1)/2).

The value C1 is output to the offset circuit 62. The offset circuit 62adds a desired digital offset value CC2 to the signal C such that thevalue C1 approximates the voltage value VR1.

In the same manner, the peak-bottom circuit 61 performs a resetoperation at a desired timing to achieve a value, which is obtained byaveraging a peak value P2 and a bottom value B2 of the next signal C,that is, a value C2 (=(P2+B2)/2). The value C2 is output to the offsetcircuit 62. The offset circuit 62 adds a desired digital offset valueCC3 to the signal C such that the value C2 approximates the voltagevalue VR1.

In this way, at the time point at which the signal having the offsetvalue added thereto finally approximates the value of the firstcomparison level VR1 of the first comparison circuit 31 in a digitalmanner as much as possible, the offset circuit 62 stops the digitaloffset addition to the signal C and holds the offset value of theprevious time.

FIG. 13 illustrates the state in which the digital offset addition isheld by the operations of the peak-bottom circuit 61 and the offsetcircuit 62, that is, a convergent state. The first comparison level VR1of the first comparison circuit 31 and the third comparison level VR3 ofthe third comparison circuit 33 have the same value.

In FIG. 13, tr1 indicates the time difference between the rising edge ofthe rectangular wave signal E and the rising edge of the rectangularwave signal G, and tf1 indicates the time difference between the fallingedge of the rectangular wave signal E and the falling edge of therectangular wave signal G. Further, tr2 and tf2 indicate the timedifference from the time point, at which the bridge signal C intersectsthe comparison level of the comparison level VR1, to the rising andfalling of the rectangular wave signal G. In FIG. 13, tr1 is smallerthan tr2 and tf1 is smaller than tf2. Consequently, both the timedifference between the rising and the falling of the rectangular wavesignal E and the time difference between the rising and the falling ofthe rectangular wave signal G are smaller than the time differencebetween the rising and the falling of a rectangular wave signal, whichare output from the first comparison circuit by DC-coupling the bridgesignal C in the case of not including the peak-bottom circuit and theoffset circuit, and the time difference between the rising and thefalling of the rectangular wave signal G.

In accordance with the magnetic detection apparatus according to thefourth embodiment of the present invention, since the time differencebetween the rising of the rectangular wave signal of the firstcomparison circuit 31 and the rising of the rectangular wave signal ofthe third comparison circuit 33 is small and the time difference betweenthe falling of the rectangular wave signal of the first comparisoncircuit 31 and the falling of the rectangular wave signal of the thirdcomparison circuit 33 is small, even if the rectangular wave signal ofthe first comparison circuit 31 is switched into the rectangular wavesignal of the third comparison circuit 33 by the selection circuit 53 orthe rectangular wave signal of the third comparison circuit 33 isswitched into the rectangular wave signal of the first comparisoncircuit 31 by the selection circuit 53, the time difference between therising positions of the rectangular wave signals and the time differencebetween the falling positions of the rectangular wave signals can bereduced, and variation in the detection accuracy of the magneticdetection apparatus due to the switching can be suppressed as much aspossible.

Various modifications and alterations of this invention will be apparentto those skilled in the art without departing from the scope and spiritof this invention, and it should be understood that this is not limitedto the illustrative embodiments set forth herein.

What is claimed is:
 1. A magnetic detection apparatus provided with asensor including magneto-electric transducers for detecting a magneticfield, the magnetic detection apparatus comprising: a first comparisonmeans that waveform-shapes a detection signal from the magneto-electrictransducers by DC coupling; a second comparison means thatwaveform-shapes the detection signal from the magneto-electrictransducers by AC coupling; an oscillation means having a naturalfrequency; a control means that counts output of the first comparisonmeans or output of the second comparison means resulting in a countvalue by using the oscillation means; and a selection means that selectsthe output of the first comparison means and the output of the secondcomparison means in response to the count value obtained by the controlmeans.
 2. The magnetic detection apparatus according to claim 1, whereinthe control means counts a time width of an output rectangular wave ofthe first comparison means or a time width of an output rectangular waveof the second comparison means by using the oscillation means, andoutputs a determination result to the selection means when it isdetermined that the counted time width is a desired time width.
 3. Themagnetic detection apparatus according to claim 2, wherein, after thecounted time width is determined as the desired time width, whenregarding from rising to next falling or next rising of the outputrectangular wave of the first comparison means or the second comparisonmeans as one time, or counts from the falling to the next rising or thenext falling of the output rectangular wave of the first comparisonmeans or the second comparison means one time, the control means outputsthe determination result to the selection means by an output rectangularwave of the first comparison means or the second comparison means afterone time or more and N times.
 4. The magnetic detection apparatusaccording to claim 2, wherein, when the control means sets a first valueto a frequency A and a second value to a frequency B, the frequency Aand the frequency B have values different from each other, the firstvalue being obtained by converting the time width of the outputrectangular wave, in which the selection means switches selection to thesecond comparison means from the first comparison means, into afrequency, and the second value being obtained by converting the timewidth of the output rectangular wave, in which the selection meansswitches selection to the first comparison means from the secondcomparison means, into a frequency.
 5. The magnetic detection apparatusaccording to claim 4, wherein the frequency A is larger than thefrequency B.
 6. The magnetic detection apparatus according to claim 1,further comprising: a peak-bottom means, provided between themagneto-electric transducers and the first comparison means, having, apeak hold means to hold a peak value of the detection signal from themagneto-electric transducers, and a bottom hold means to hold a bottomvalue of the detection signal from the magneto-electric transducers,that outputs a desired value by the peak value and the bottom value; andan offset generation means that applies an offset value to the detectionsignal by the value output from the peak-bottom means.
 7. The magneticdetection apparatus according to claim 6, wherein the value output fromthe peak-bottom means is an average value of the peak value and thebottom value.
 8. The magnetic detection apparatus according to claim 1,wherein the magneto-electric transducers include magnetic reluctanceelements.
 9. The magnetic detection apparatus according to claim 1,wherein the magneto-electric transducers include giant magneticreluctance elements (GMR elements).